Possible cheater

So she came home one day with this thumbprint size bruise on her arm (she tried to say it came from me but we had no sex in almost a week) fingernail scratches on the middle of her upper back (she said she did it herself at which point she showed me I can see this being possible) she got mad at me when I questioned her about it and told me to check her underwear. I didn't actually check until the next day but there was white dried crusty's. She also checked my phone a lot my messages gets mad at me whenever I talk to my ex who I share a child with. I know there's a guy at her work that she had feelings for I don't know if that's still an issue being that her work is nothing but guys. Yes she has had sexual contact with this man but only before she met me that I know of. Should I be concerned?